ΔE 24.3, loose: different enough that you should pick on purpose. Mournfang Brown is noticeably darker, much more saturated, cooler than Battle of Marathon.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 24). Mournfang Brown is noticeably darker, much more saturated, cooler than Battle of Marathon.
The same difference applies the other way round: Battle of Marathon is noticeably lighter, much more muted, warmer.
ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.
See Battle of Marathon on the colour wheel See Mournfang Brown on the colour wheel
All matches: Battle of Marathon equivalents · Mournfang Brown equivalents